The preparation of IPDA by aminating hydrogenation of IPN is known and has already been described many times.
In the simplest case (U.S. Pat. No. 3,352,913 A), IPN is reacted in the presence of hydrogen and of an excess of ammonia over a cobalt catalyst. IPN and ammonia initially react with elimination of water to form isophoronenitrile imine, IPNI, which is subsequently hydrogenated to IPDA.

When the reaction is conducted in this way, the yield of IPDA is determined to a crucial degree by the excess of ammonia. The maximum IPDA yields achieved are about 80%. The main by-product is what is called the amino alcohol, IPAA, which results from the direct hydrogenation of the IPN.

A significant rise in the IPDA yield is achieved when the formation of IPNI is accelerated by use of suitable imination catalysts. Suitable imination catalysts are, for example, acidic ion exchange resins (EP 0 042 119 B1). In addition, it is also possible to use acidic metal oxides (EP 0 449 089 B1), sulphonic acid group-containing organopolysiloxanes (EP 0 816 323 A1), heteropolyacids (DE 44 26 472 A1) and activated carbon (EP 0 623 585 A1) as imination catalysts. As well as the reduction of the unwanted amino alcohol, other by-products are also distinctly suppressed, for example bicyclic compounds and those by-products which result from the elimination of HCN.